1. Field of the Invention
The present invention relates generally to a sprouted vegetable seeds sterilizing method and more particularly to a sterilizing method for destroying bacteria existing on raw material seeds in the process of cultivating sprouted vegetables, for example various kinds of sprouts such as black mung bean sprouts, mung bean sprouts, soybean sprouts or alfalfa sprouts, and KAIWARE radish or the like, said bacteria including not only microorganisms breeding during the cultivation of the sprouted vegetables to damage their growth or to putrefy them but also germs, such as food poisoning germs to cause food poisoning when the sprouted vegetables after harvested are eaten, or the like.
2. Description of the Prior Art
In cultivating the sprouted vegetables wherein seeds of various kinds of sprouts are sprouted to grow slightly to be good for eating, it is important to promote their rearing while restraining breeding of harmful bacteria. Also, as these sprouted vegetables are often eaten fresh or half-cooked, it is needed to make lessened various kinds of microorganisms or germs, such as food poisoning germs, sticking to the sprouted vegetables as harvested.
Especially, while the sprouted vegetables are cultivated at a temperature and humidity suitable for their sprouting and growth, such rearing environment is also an environment suitable for breeding of various kinds of microorganisms or germs. Hence, in rearing the sprouted vegetables, it is important to ensure such condition that the microorganisms, even in a small quantity, sticking to the seeds of the sprouted vegetables are removed sufficiently.
In terms of poisoning from eating of alfalfa sprouts or the like, it is known that microorganisms or germs coming from their raw material seeds relate thereto. These micro-organisms or germs are considered to come from contamination by excrement of wild animals at farms where the seeds are harvested or by small animals, such as rats, while the seeds are stored.
There are often seen accidents of poisoning from eating of alfalfa sprouts in countries of America and Europe and countermeasures therefor are being seeked variously. As seeds of the alfalfa sprouts are harvested by machinery and their shells are weak comparatively to be broken easily, even in a case of contamination by disease germs from outside, it is considered that interiors of the seeds are contaminated and in this case, there is a possibility that the contamination has come up to inside of the shells or embryos of the seeds.
Conventionally, sterilization of the seeds has been done in such way that chemicals of hypochloric acid or the like are used or the seeds are dipped in a hot water of about 60 to 70xc2x0 C. for a few minutes. However, there have been some cases where the effect of the sterilization is not obtained sufficiently even by use of a high concentration hypochloric acid and this is considered because the contamination has spread to the interiors of the seeds, as mentioned above.
It is difficult to destroy microorganisms or germs without damaging life activities of the seeds to sprout and grow as a living thing and in addition, it is not permitted to use strong chemicals because sprouted vegetables are foods which are often eaten fresh or half-cooked.
Under the mentioned circumstances, the present applicant has heretofore disclosed a new method in the Japanese laid-open patent application No. Hei 6-261634 to perform a sterilization effectively of microorganisms or germs existing on outer surfaces or inner surfaces of outer shells of the sprouted vegetable seeds by bringing all the seeds into contact uniformly for a controlled time with a high temperature adjusted to such a temperature condition as not to damage living powers of the seeds. However, in the case of the seeds having damages on their shells (damaged seeds) as mentioned above, there is found a problem that a sterilization cannot be done sufficiently even if they are treated by a sufficient thermal treatment condition.
In view of the problem in the prior art, it is an object of the present invention to provide a sprouted vegetable seeds sterilizing method by which the above-mentioned sprouted vegetable seeds sterilization disclosed by the present applicant can be done effectively and also especially food poisoning germs can be destroyed.
Based on the fact that even if an accurate thermal sterilization has been done for the sprouted vegetable seeds, food poisoning germs have not been destroyed completely, the inventors here have pursued the cause therefor and found that according to a lot of raw material seeds, the shells are largely damaged so that the food poisoning germs encroach up to interiors of the seeds and this is the reason why the thermal sterilization has been insufficient.
Thus, in order to destroy the food poisoning germs which have encroached up to insides of the shells, the present invention provides a sprouted vegetable seeds sterilizing method comprising steps of; pre-soaking the sprouted vegetable seeds in water; then pre-heating them; then exposing them to a high temperature for a short time for sterilization; and a cooling them.
In the sprouted vegetable seeds sterilizing method of the present invention, the pre-soaking which is to be done before the thermal sterilizing treatment is needed to be carried out at a temperature which is as low as possible in order not to damage embryos in the subsequent thermal sterilizing treatment and also to be carried out in an accurate and suitable temperature and time in order to make the sterilization in the high temperature sterilizing treatment effective. In terms of the temperature and time of the pre-soaking, there are optimum values thereof according to the kinds of the sprouted vegetable seeds and the place and year of harvest thereof and while being needed to be selected suitable, the pre-soaking is generally in the range of 30 to 60 minutes at a temperature of 5 to 25xc2x0 C. The accurate pre-soaking can be judged by measuring a water absorption of the seeds after soaking them in water.
Also, in the sprouted vegetable seeds sterilizing method of the present invention, while the temperature and time of the pre-heating are needed to be selected according to the sprouted vegetable seeds, the pre-heating is generally in the range of 10 to 30 seconds at a temperature of 40 to 80xc2x0 C.
The temperature and time of the high temperature sterilizing treatment are also needed to be selected suitably according to the sprouted vegetable seeds but the high temperature sterilizing treatment is generally in the range of 10 to 120 seconds at a temperature of 70 to 90xc2x0 C. Also, as to the temperature and time of the cooling, they are needed to be selected according to the sprouted vegetable seeds and it is effective to do the cooling immediately after the high temperature sterilizing treatment at temperature of 15 to 25xc2x0 C. generally.
In the pre-soaking of the present invention, it is possible to add a low concentration sterilizing agent of hypochloric acid, chlorine, ethanol or the like or to use an ozone water. Also, in the cooling treatment after the high temperature sterilization, it is effective to enhance the sterilizing effect further by using a hypochloric acid water solution or ozone water.
In the thermal sterilizing treatment method according to the present invention, as mentioned above, the sprouted vegetable seeds are pre-soaked in water so that the shells are swollen to improve the heat transfer to the shell interiors and also to remove bubbles existing between the shells and the embryos, thereby the heat of the subsequent high temperature treatment encroaches from damaged portions of the shells and the food poisoning germs existing inside of the shells can be destroyed efficiently by the heat.
Also, the low temperature water is used in the pre-soaking, thereby a damage which the embryos may receive in the subsequent high temperature treatment can be mitigated and lowering of a sprouting rate due to the high temperature treatment can be suppressed.
In the thermal sterilizing treatment method according to the present invention as mentioned above, as the sprouted vegetable seeds are treated by the pre-soaking and then by the thermal sterilization, the sprouted vegetable seeds which have been swollen by the pre-soaking become in the state where the outside heat is easy to transfer therein and the thermal sterilizing treatment to be then carried out can be perfected uniformly to the entire interiors of the sprouted vegetable seeds as well as the damage which the embryos may receive in the subsequent high temperature treatment can be mitigated.
Thus, according to the sterilizing method of the present invention, the thermal sterilizing treatment before rearing the seeds is perfected so that the seeds are reared in an almost completely sterilized state, hence there occurs no case of the microorganisms breeding to obstruct a normal rearing of the sprouted vegetables or to putrefy them and also there is no case of the food poisoning germs sticking to the sprouted vegetables as harvested, thereby the sprouted vegetables can be served safely for eating.